The invention concerns a superconducting magnet configuration with a magnet coil of inductance L, which is disposed in a cryostat at a cryogenic temperature to generate a temporally stable magnetic field, in a working volume, suitable for NMR measurements, and with current feed lines to an external current source, via which a current of current strength IPS can be supplied, wherein the inductance at cryogenic temperatures can be exclusively short-circuited via a switch.
A magnet configuration of this type is disclosed In DE 102 41 966.
Superconducting magnet coils that generate a stable magnetic field are required for a plurality of applications in research and medicine, in particular for NMR apparatus. For this reason, the field drift of the magnet coil should be minimized.
The magnet coil disclosed in DE 102 41 966 can be short-circuited via a superconducting switch which is connected in series with a resistance. During operation, the magnet coil is constantly supplied with current from a current source to generate a desired magnetic field in a working volume and to keep the sum of voltages in the circuit at zero and thereby also the magnetic field drift.
This configuration is disadvantageous, since superconducting switches tend to immediately quench at high currents. During a quench, the current circulating in the magnet coil must be discharged quickly via an external resistor thereby producing a very large discharge voltage, which is also present at the superconducting switch. This can easily destroy the superconducting switch. In order to prevent this, a large number of long switch wires are generally required to carry the current, without being damaged. However, this increases the amount of material required.
Another solution is to embed the superconducting wire of the switch in a CuNi matrix in order to obtain a high resistance using little wire. These wires are, however, very unstable and are therefore suitable for the above-mentioned application only to a limited degree.
The use of superconducting switches is conventionally preferred, since it yields an almost infinite time constant to ensure stable operation of the magnet configuration.
It is the underlying object of the invention to propose a superconducting magnet configuration which ensures stable permanent operation via mains supply even at high currents (>1000 A) with little technical expense, and effectively discharges the energy released during a quench.